Heretofore, a welding system for welding vehicle body frames, for example, has a plurality of welding stations with welding robots. Vehicle body frames are positioned on jigs, and are supplied from a workpiece feed path to the respective welding stations where the vehicle body frames are welded.
Jigs for positioning the vehicle body frames in the welding stations are required for each of the various respective vehicle body frames. The positioning relationship between the vehicle body frames supplied to the welding stations and the welding robot differs depending on the combinations of the types of the vehicle body frames and the types of the jigs and welding robots corresponding to the vehicle body frames. Therefore, it is necessary to provide as many dedicated jigs as the number of the combinations. As the number of types of vehicle body frames and the number of types of welding robots increase, more types of jigs are required, resulting in an increase in the cost of the facilities. Furthermore, since the positional relationship between each jig and each welding robot needs to be adjusted once in every two or three months, the management process for maintaining positional accuracy is complicated and troublesome.
According to a conventional arrangement disclosed in Japanese Patent No. 3351753, for example, each welding station has a positionally adjustable positioner positioning a vehicle body frame, and a vehicle body frame is supplied from a workpiece feed path to each positioner by a feed robot. The vehicle body frame is adjusted to a position and attitude depending on the welding robot and then welded by the welding robot. The positioners disposed in the respective welding stations can be commonly designed for use with the welding robots in the respective welding stations.
However, it is essential for each welding station to have its own positioner, and at least positioners of different structures depending on the types of vehicle body frames are required.